Method for manufacturing press-hardened laser-welded steel parts and press-hardened laser-welded steel parts

Abstract

This invention provides a method for manufacturing welded steel blanks from two pre-coated plates, which enables the production of parts with satisfactory impact performance characteristics after press hardening, even with relatively high aluminum content in the welded joints, at a relatively low cost. [Solution] Provide first and second pre-coated steel sheets (1, 2), butt weld the first and second pre-coated steel sheets (1) together to obtain a blank (15), and weld the blank (15) at a minimum temperature T at least 10°C lower than the complete austenitization temperature of the welded joint (22). min A method comprising heating to a heat treatment temperature at least 15°C higher, holding the blank (15) at the heat treatment temperature for a time between 2 and 10 minutes, press-forming the blank (15) into a part, and cooling.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a press-hardened laser-welded steel part and a press-hardened laser-welded steel part thus obtained.

Background Art

[0002] This type of steel part is used particularly in the automotive industry, and more specifically, for manufacturing collision management parts such as intrusion prevention or shock absorption parts, structural parts, or parts that contribute to the safety of an automobile.

[0003] For this type of part, automobile manufacturers have instructed that the weld joint should not constitute the weakest zone of the welded steel part.

[0004] To prevent corrosion, the steel sheet used for manufacturing such welded steel parts is pre-coated with an aluminum-based precoat through hot dip coating in an aluminum-containing bath. When welding the steel sheet without prior preparation, the aluminum-based precoat is diluted in the molten metal by the steel substrate during the welding operation. Aluminum tends to raise the complete austenitization temperature of the molten metal, thus preventing complete transformation to austenite during hot forming using conventional heat treatment temperatures. As a result, it may no longer be possible to obtain a fully martensite or bainite microstructure in the weld joint during press cooling performed during the hot forming process.

[0005] Furthermore, it is impossible to use a higher heat treatment temperature that would enable complete austenitization of the weld joint, because it would result in over-alloying of the coating that would potentially have a negative impact on the paint adhesion and / or the spot weldability of the press-hardened part.

[0006] Faced with this situation, when manufacturing parts from such pre-coated steel sheets, two solutions have been developed in the prior art to enable the acquisition of a complete martensitic structure in hot forming and welded joints after quenching using conventional heat treatment temperatures.

[0007] In particular, EP2007545 describes a first solution that involves removing the surface layer of the metal alloy at the welded end of the pre-coated steel sheet in order to significantly reduce the total aluminum content in the welded joint and thereby obtain a complete austenitization temperature close to the complete austenitization temperature of the base material of the pre-coated steel sheet.

[0008] Furthermore, EP2737971, US2016 / 0144456, and WO2014075824 describe a second solution which involves welding pre-coated steel sheets using a filler wire containing an austenite-stabilizing element such as carbon, manganese, or nickel to counteract the presence of aluminum in the welded joint and lower its complete austenitization temperature, thereby obtaining a complete martensitic structure in the welded joint after hot forming and quenching using conventional heat treatment temperatures.

[0009] However, these methods are not entirely satisfactory.

[0010] In fact, the first solution is relatively time-consuming. Furthermore, the second method may require the addition of a relatively large amount of austenite-forming elements to obtain a complete martensitic structure in the welded joint after heat treatment. This addition increases manufacturing costs and can lead to problems such as unsatisfactory joint geometry or heterogeneous mixing of materials from the pre-coated steel sheet and the filler wire in the welded joint, along with the risk of locally retained austenite. [Prior art documents] [Patent Documents]

[0011] [Patent Document 1] European Patent Application Publication No. 2007545 Specification [Patent Document 2] European Patent Application Publication No. 2737971 [Patent Document 3] U.S. Patent Application Publication No. 2016 / 0144456 [Patent Document 4] International Publication No. 2014 / 075824 [Overview of the project] [Problems that the invention aims to solve]

[0012] Therefore, the object of the present invention is to provide a method for manufacturing a welded steel blank from two pre-coated plates that enables the production of a component with satisfactory impact performance characteristics after press hardening, even with a relatively high aluminum content in the welded joint, at a relatively low cost. [Means for solving the problem]

[0013] For this purpose, the present invention comprises the following sequential steps, namely - A step of providing a first pre-coated steel sheet and a second pre-coated steel sheet, wherein each of the first and second pre-coated steel sheets comprises a steel base material, and at least one of the first and second pre-coated steel sheets has an aluminum-containing pre-coat containing at least 50% by weight of aluminum on at least one of its main surfaces. The first pre-coated steel sheet has a first thickness, and the second pre-coated steel sheet has a second thickness. The base material of the first pre-coated steel sheet has a maximum tensile strength that is strictly greater than the maximum tensile strength of the base material of the second pre-coated steel sheet after press curing, after press curing. The process provides a method in which the product of the first thickness and the maximum tensile strength of the first pre-coated steel sheet after press hardening is strictly greater than the product of the second thickness and the maximum tensile strength of the second pre-coated steel sheet, then, - A step of removing aluminum-containing precoat from at least one main surface on at least one weld edge or edge to be welded of the first and second precoated steel sheets provided in the providing step, over at least a portion of its thickness, provided that the theoretical average aluminum content in the welded joint obtained by butt welding the first and second precoated steel sheets provided in the providing step is strictly greater than 1.25% by weight, optionally using a filler material containing at least 0.05% by weight of aluminum, wherein as a result the theoretical average aluminum content in the welded joint obtained by butt welding the first and second precoated steel sheets thus produced, optionally using a filler material containing at least 0.05% by weight of aluminum, falls between 0.5% by weight and 1.25% by weight. - A welding process comprising butt welding a first pre-coated steel sheet and a second pre-coated steel sheet using laser welding to obtain a welded joint between the first and second pre-coated steel sheets, thereby obtaining a weld blank, wherein the welding process may include the use of filler material, a butt welding process. - A step of heating the welding blank to a heat treatment temperature, wherein the heat treatment temperature is at least 10°C lower than the complete austenitization temperature of the welded joint, and the minimum temperature T min At least 15°C higher, here,

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[0014] According to a particular embodiment of the method, - The process of removing the aluminum-containing precoat is performed in the following cases: - If a filler material containing up to 0.05% by weight of aluminum is used, and the welded joint obtained by butt welding the first and second pre-coated steel plates provided in the supplying process is to be more than 1.25% by weight, And optionally, a filler material containing up to 0.05% by weight of aluminum may be used, and the theoretical average aluminum content of the welded joint obtained by butt welding the first and second pre-coated steel plates provided in the supplying process will be between 0.5% by weight and 1.25% by weight, and more specifically, if it exceeds 0.5% by weight, This process is carried out using a filler material containing up to 0.05% by weight of aluminum, in some cases, so that the theoretical average aluminum content of the welded joint obtained by butt welding the first and second pre-coated steel plates thus prepared falls between 0.5% by weight and 1.25% by weight.

[0015] - At the end of the heating process, the microstructure of the substrates of the first and second pre-coated steel sheets is completely austenite. - The ratio of the maximum tensile strength of the base material of the first pre-coated steel sheet after press hardening to the maximum tensile strength of the base material of the second pre-coated steel sheet after press hardening is 1.2 or greater.

[0016] - The carbon content of the base material of the first pre-coated steel sheet is at least 0.05% by weight higher than the carbon content of the base material of the second pre-coated steel sheet.

[0017] - Each of the first and second pre-coated steel sheets provided in the supplying process includes an aluminum-containing pre-coat containing at least 50% by weight of aluminum on at least one of its main surfaces.

[0018] - The first and second pre-coated steel sheets provided in the supply process include an aluminum-containing pre-coat on both of their main surfaces, which contains at least 50% by weight of aluminum.

[0019] -During butt welding, the aluminum-containing precoat remains completely present on both main surfaces of at least one of the first precoated steel sheet and the second precoated steel sheet, for example, on each of the first and second precoated steel sheets.

[0020] - The method further includes a step of creating a weld edge of at least one of the first and second pre-coated steel sheets, which is intended to be incorporated at least partially into the weld joint, by removing the aluminum-containing pre-coat on at least one of its main surfaces over at least a portion of its thickness, even if the theoretical average aluminum content of the weld joint obtained by butt welding the first and second pre-coated steel sheets provided in the providing step is between 0.5% and 1.25% by weight, optionally using a filler material containing up to 0.05% by weight of aluminum,

[0021] - The method further includes a step of creating a weld edge of at least one of the first and second pre-coated steel sheets, which is intended to be incorporated at least partially into the weld joint, by removing at least a portion of the thickness of the aluminum-containing pre-coat on at least one of its main surfaces before butt welding, even if the theoretical average aluminum content of the weld joint obtained by butt welding the first and second pre-coated steel sheets provided in the providing step is between 0.5% and 1.25% by weight, and the removal step is carried out by optionally using a filler material containing up to 0.05% by weight of aluminum, such that the theoretical average aluminum content of the weld joint obtained by butt welding the first and second pre-coated steel sheets thus created is between 0.5% and 1.25% by weight.

[0022] - For at least one of the first and second pre-coated steel sheets, the steel of the base material is by weight, 0.10% ≤ C ≤ 0.5% 0.5% ≤ Mn ≤ 3% 0.1% ≤ Si ≤ 1% 0.01% ≤ Cr ≤ 1% Ti ≤ 0.2% Al ≤ 0.1% S ≤ 0.05% P ≤ 0.1% B ≤ 0.010% It contains iron and impurities resulting from the manufacturing process.

[0023] - For at least one of the first and second pre-coated steel sheets, the steel of the base material is by weight, 0.15% ≤ C ≤ 0.25% 0.8% ≤ Mn ≤ 1.8% 0.1% ≤ Si ≤ 0.35% 0.01% ≤ Cr ≤ 0.5% Ti ≤ 0.1% Al ≤ 0.1% S ≤ 0.05% P ≤ 0.1% B ≤ 0.005% It contains iron and impurities resulting from the manufacturing process.

[0024] - For at least one of the first and second pre-coated steel sheets, the steel of the base material is by weight, 0.040% ≤ C ≤ 0.100% 0.70% ≤ Mn ≤ 2.00% Si ≤ 0.50% S ≤ 0.009% P ≤ 0.030% 0.010% ≤ Al ≤ 0.070% 0.015% ≤ Nb ≤ 0.100% Ti ≤ 0.080% N ≤ 0.009% Cu ≤ 0.100% Ni ≤ 0.100% Cr ≤ 0.2% Mo ≤ 0.100% Ca ≤ 0.006% It contains iron and impurities resulting from the manufacturing process.

[0025] - For at least one of the first and second pre-coated steel sheets, the steel of the base material is by weight, 0.06% ≤ C ≤ 0.100% 1.4% ≤ Mn ≤ 1.9% 0.2% ≤ Si ≤ 0.5% 0.010% ≤ AI ≤ 0.070% 0.04% ≤ Nb ≤ 0.06% 3.4 × N ≤ Ti ≤ 8 × N 0.02% ≤ Cr ≤ 0.1% 0.0005% ≤ B ≤ 0.004% 0.001% ≤ S ≤ 0.009% It contains iron and impurities resulting from the manufacturing process.

[0026] - For at least one of the first and second pre-coated steel sheets, the steel of the base material is by weight, 0.24% ≤ C ≤ 0.38% 0.40% ≤ Mn ≤ 3% 0.10% ≤ Si ≤ 0.70% 0.015% ≤ AI ≤ 0.070% 0% ≤ Cr ≤ 2% 0.25% ≤ Ni ≤ 2% 0.015% ≤ Ti ≤ 0.10% 0% ≤ Nb ≤ 0.060% 0.0005% ≤ B ≤ 0.0040% 0.003% ≤ N ≤ 0.010% 0.0001% ≤ S ≤ 0.005% 0.0001% ≤ P ≤ 0.025% It contains, and the titanium and nitrogen content satisfies the following relationship: Ti / N > 3.42 The carbon, manganese, chromium, and silicon content satisfies the following relationship:

number

[0027] - Laser welding is performed using protective gases, particularly helium and / or argon, and

[0028] - The first and second pre-coated steel sheets have different thicknesses.

[0029] The present invention further relates to a press-hardened laser-welded steel part, wherein the steel part includes a first coated steel part portion and a second coated steel part portion. Each coated steel component includes a steel base material, and at least one of the first coated steel component and the second coated steel plate has an aluminum-containing coating containing at least 30% by weight of aluminum on at least one of its main surfaces. The first coated steel component has a first thickness, the second coated steel plate has a second thickness, the base material of the first coated steel component has a maximum tensile strength that is strictly greater than the maximum tensile strength of the base material of the second coated steel component, the product of the first thickness and the maximum tensile strength of the first coated steel component is strictly greater than the product of the second thickness and the maximum tensile strength of the second coated steel component. The first and second coated steel component parts are joined by a welded joint, the welded joint having an aluminum content between 0.5% and 1.25% by weight, the microstructure of the welded joint containing martensite and / or bainite, and including a ferrite fraction with a ferrite fraction of 15% to a maximum ferrite fraction of -5%, the maximum ferrite fraction of the

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[0030] According to a particular embodiment of the steel component, the ratio of the maximum tensile strength of the base material of the first coated steel component portion to the maximum tensile strength of the base material of the second coated steel component portion is 1.2 or greater.

[0031] - For at least one of the first and second coated steel component parts, the base steel is by weight, 0.10% ≤ C ≤ 0.5% 0.5% ≤ Mn ≤ 3% 0.1% ≤ Si ≤ 1% 0.01% ≤ Cr ≤ 1% Ti ≤ 0.2% Al ≤ 0.1% S ≤ 0.05% P ≤ 0.1% B ≤ 0.010% It contains iron and impurities resulting from the manufacturing process.

[0032] - For at least one of the first and second coated steel component parts, the base steel is by weight, 0.15% ≤ C ≤ 0.25% 0.8% ≤ Mn ≤ 1.8% 0.1% ≤ Si ≤ 0.35% 0.01% ≤ Cr ≤ 0.5% Ti ≤ 0.1% Al ≤ 0.1% S ≤ 0.05% P ≤ 0.1% B ≤ 0.005% It contains iron and impurities resulting from the manufacturing process.

[0033] - For at least one of the first and second coated steel component parts, the base steel is by weight, 0.040% ≤ C ≤ 0.100% 0.70% ≤ Mn ≤ 2.00% Si ≤ 0.50% S ≤ 0.005% P ≤ 0.030% 0.010% ≤ Al ≤ 0.070% 0.015% ≤ Nb ≤ 0.100% Ti ≤ 0.080% N ≤ 0.009% Cu ≤ 0.100% Ni ≤ 0.100% Cr ≤ 0.2% Mo ≤ 0.100% Ca ≤ 0.006% It contains iron and impurities resulting from the manufacturing process.

[0034] - For at least one of the first and second coated steel component parts, the base steel is by weight, 0.24% ≤ C ≤ 0.38% 0.40% ≤ Mn ≤ 3% 0.10% ≤ Si ≤ 0.70% 0.015% ≤ AI ≤ 0.070% 0% ≤ Cr ≤ 2% 0.25% ≤ Ni ≤ 2% 0.015% ≤ Ti ≤ 0.10% 0% ≤ Nb ≤ 0.060% 0.0005% ≤ B ≤ 0.0040% 0.003% ≤ N ≤ 0.010% 0.0001% ≤ S ≤ 0.005% 0.0001% ≤ P ≤ 0.025% It contains, and the titanium and nitrogen content satisfies the following relationship: Ti / N > 3.42 The carbon, manganese, chromium, and silicon content satisfies the following relationship:

number

[0035] - For at least one of the first and second coated steel component parts, the base steel is by weight, 0.06% ≤ C ≤ 0.100% 1.4% ≤ Mn ≤ 1.9% 0.2% ≤ Si ≤ 0.5% 0.010% ≤ AI ≤ 0.070% 0.04% ≤ Nb ≤ 0.06% 3.4 × N ≤ Ti ≤ 8 × N 0.02% ≤ Cr ≤ 0.1% 0.0005% ≤ B ≤ 0.004% 0.001% ≤ S ≤ 0.009% It contains [a certain substance], with the remainder being iron and impurities resulting from the manufacturing process.

[0036] The present invention will be better understood by reading the following specification, which is given only as an example, with reference to the accompanying figures. [Brief explanation of the drawing]

[0037] [Figure 1] This is a schematic cross-sectional view of the start of the welding process of the method according to the present invention. [Figure 2] This is a schematic cross-sectional view of the welded blank obtained at the end of the welding process. [Figure 3] This is a perspective view of a pre-coated steel sheet after the manufacturing process. [Modes for carrying out the invention]

[0038] In the entire patent application, the elemental content is expressed as weight percent (weight%).

[0039] This invention relates to a method for manufacturing press-hardened laser-welded steel parts.

[0040] More specifically, the method includes a first step of providing a first pre-coated steel sheet 1 and a second pre-coated steel sheet 2.

[0041] Each pre-coated steel sheet 1, 2 has two opposing main surfaces 5, 6 and at least one side surface 13 extending from one main surface 5, 6 to the other between the two opposing main surfaces 5, 6. In the example shown in Figure 3, the pre-coated steel sheets 1, 2 have four side surfaces 13. For example, the side surface 13 forms an angle with one of the main surfaces 5, 6 that falls between 60° and 90°.

[0042] As shown in Figure 1, each pre-coated steel sheet 1, 2 includes a metal substrate 3, 4 having an aluminum-containing pre-coat 7, 8 on at least one of its main surfaces. The pre-coats 7, 8 are superimposed on and in contact with the substrates 3, 4.

[0043] The metal substrates 3 and 4 are, more specifically, steel substrates.

[0044] Furthermore, the steel of the base materials 3 and 4 is, more specifically, steel having a ferrito-perlitic microstructure.

[0045] Preferably, the base materials 3 and 4 are made of steel intended for heat treatment, more specifically, press-hardenable steel, such as manganese-boron steel like 22MnB5 type steel.

[0046] According to one embodiment, the steel of the base materials 3 and 4 is by weight 0.10% ≤ C ≤ 0.5% 0.5% ≤ Mn ≤ 3% 0.1% ≤ Si ≤ 1% 0.01% ≤ Cr ≤ 1% Ti ≤ 0.2% Al ≤ 0.1% S ≤ 0.05% P ≤ 0.1% B ≤ 0.010% It contains [a certain substance], with the remainder being iron and impurities resulting from the manufacturing process.

[0047] More specifically, the steel of base materials 3 and 4 is by weight 0.15% ≤ C ≤ 0.25% 0.8% ≤ Mn ≤ 1.8% 0.1% ≤ Si ≤ 0.35% 0.01% ≤ Cr ≤ 0.5% Ti ≤ 0.1% Al ≤ 0.1% S ≤ 0.05% P ≤ 0.1% B ≤ 0.005% It contains [a certain substance], with the remainder being iron and impurities resulting from the manufacturing process.

[0048] According to the alternative, the steel of base materials 3 and 4 is by weight 0.040% ≤ C ≤ 0.100% 0.70% ≤ Mn ≤ 2.00% Si ≤ 0.50%, or more specifically, Si ≤ 0.30%. S ≤ 0.009%, or more specifically, S ≤ 0.005%. P ≤ 0.030% 0.010% ≤ Al ≤ 0.070% 0.015% ≤ Nb ≤ 0.100% Ti ≤ 0.080% N ≤ 0.009% Cu ≤ 0.100% Ni ≤ 0.100% Cr ≤ 0.2% Mo ≤ 0.100% Ca ≤ 0.006% It contains [a certain substance], with the remainder being iron and impurities resulting from the manufacturing process.

[0049] According to the alternative, the steel of base materials 3 and 4 is by weight 0.24% ≤ C ≤ 0.38% 0.40% ≤ Mn ≤ 3% 0.10% ≤ Si ≤ 0.70% 0.015% ≤ AI ≤ 0.070% 0% ≤ Cr ≤ 2% 0.25% ≤ Ni ≤ 2% 0.015% ≤ Ti ≤ 0.10% 0% ≤ Nb ≤ 0.060% 0.0005% ≤ B ≤ 0.0040% 0.003% ≤ N ≤ 0.010% 0.0001% ≤ S ≤ 0.005% 0.0001% ≤ P ≤ 0.025% It contains, and the titanium and nitrogen content satisfies the following relationship: Ti / N > 3.42 The carbon, manganese, chromium, and silicon content satisfies the following relationship:

number

[0050] According to the alternative, the steel of base materials 3 and 4 is by weight 0.06% ≤ C ≤ 0.100% 1.4% ≤ Mn ≤ 1.9% 0.2% ≤ Si ≤ 0.5% 0.010% ≤ AI ≤ 0.070% 0.04% ≤ Nb ≤ 0.06% 3.4 × N ≤ Ti ≤ 8 × N 0.02% ≤ Cr ≤ 0.1% 0.0005% ≤ B ≤ 0.004% 0.001% ≤ S ≤ 0.009% It contains [a certain substance], with the remainder being iron and impurities resulting from the manufacturing process.

[0051] The base materials 3 and 4 can be obtained, depending on their desired thickness, by hot rolling and / or cold rolling followed by annealing, or by other suitable methods.

[0052] The base materials 3 and 4 have a thickness that is advantageously between 0.6 mm and 5 mm, more specifically between 0.8 mm and 5 mm, and even more specifically between 1.0 mm and 2.5 mm.

[0053] For example, the thickness of the base material 3 of the first pre-coated steel sheet 1 is different from the thickness of the base material 4 of the second pre-coated steel sheet 2.

[0054] According to the alternative plan, the base materials 3 and 4 of the first and second pre-coated steel sheets 1 and 2 have the same thickness.

[0055] According to the present invention, the base material 3 of the first pre-coated steel sheet 1 has a maximum tensile strength Ts1 that is strictly greater than the maximum tensile strength Ts2 of the base material 4 of the second pre-coated steel sheet 2 after press curing, after press curing.

[0056] In this context, "after press hardening" refers to the period after the steel substrate has been heated to a temperature above the complete austenitization temperature Ac3, hot-pressed to achieve hardening compared to its initial state, and then cooled.

[0057] For example, the maximum tensile strength Ts1 of the base material 3 of the first pre-coated steel sheet 1 after press hardening is between 1400 MPa and 1600 MPa or between 1700 MPa and 2000 MPa.

[0058] For example, the maximum tensile strength Ts2 of the base material 3 of the second pre-coated steel sheet 2 after press hardening falls between 500 MPa and 700 MPa or between 1000 MPa and 1200 MPa.

[0059] For example, the ratio (Ts1 / Ts2) of the maximum tensile strength Ts1 of the base material 3 of the first pre-coated steel sheet 1 after press hardening to the maximum tensile strength Ts2 of the base material 4 of the second pre-coated steel sheet 2 after press hardening is 1.2 or greater, more specifically 1.4 or greater.

[0060] Furthermore, the first pre-coated steel sheet 1 has a first thickness t1. The second pre-coated steel sheet 1 has a second thickness t2.

[0061] Thicknesses t1 and t2 are, for example, between 0.6 mm and 5 mm, more specifically between 0.8 mm and 5 mm, and even more specifically between 1.0 mm and 2.5 mm.

[0062] According to one embodiment, thicknesses t1 and t2 are the same. According to an alternative, thicknesses t1 and t2 are different.

[0063] The product of the first thickness t1 and the maximum tensile strength Ts1 of the first pre-coated steel sheet 1 is strictly greater than the product of the second thickness t2 and the maximum tensile strength Ts2 of the second pre-coated steel sheet 1.

[0064] In particular, the compositions of the base materials 3 and 4 of the first and second pre-coated steel sheets 1 and 2 are selected from the above compositions.

[0065] For example, the steel of the base material 3 of the first pre-coated steel sheet 1 is by weight 0.15% ≤ C ≤ 0.25% 0.8% ≤ Mn ≤ 1.8% 0.1% ≤ Si ≤ 0.35% 0.01% ≤ Cr ≤ 0.5% Ti ≤ 0.1% Al ≤ 0.1% S ≤ 0.05% P ≤ 0.1% B ≤ 0.005% It contains [a certain substance], with the remainder being iron and impurities resulting from the manufacturing process.

[0066] In another example, the steel of the base material 3 of the first pre-coated steel sheet 1 is by weight 0.24% ≤ C ≤ 0.38% 0.40% ≤ Mn ≤ 3% 0.10% ≤ Si ≤ 0.70% 0.015% ≤ AI ≤ 0.070% 0% ≤ Cr ≤ 2% 0.25% ≤ Ni ≤ 2% 0.015% ≤ Ti ≤ 0.10% 0% ≤ Nb ≤ 0.060% 0.0005% ≤ B ≤ 0.0040% 0.003% ≤ N ≤ 0.010% 0.0001% ≤ S ≤ 0.005% 0.0001% ≤ P ≤ 0.025% It contains, and the titanium and nitrogen content satisfies the following relationship: Ti / N > 3.42 The carbon, manganese, chromium, and silicon content satisfies the following relationship:

number

[0067] For example, the steel of the base material 4 of the second pre-coated steel sheet 2 is by weight 0.040% ≤ C ≤ 0.100% 0.70% ≤ Mn ≤ 2.00% Si ≤ 0.50%, or more specifically, Si ≤ 0.30%. S ≤ 0.009%, or more specifically, S ≤ 0.005%. P ≤ 0.030% 0.010% ≤ Al ≤ 0.070% 0.015% ≤ Nb ≤ 0.100% Ti ≤ 0.080% N ≤ 0.009% Cu ≤ 0.100% Ni ≤ 0.100% Cr ≤ 0.2% Mo ≤ 0.100% Ca ≤ 0.006% It contains [a certain substance], with the remainder being iron and impurities resulting from the manufacturing process.

[0068] In another example, the steel of the base material 4 of the second pre-coated steel sheet 2 is by weight 0.06% ≤ C ≤ 0.100% 1.4% ≤ Mn ≤ 1.9% 0.2% ≤ Si ≤ 0.5% 0.010% ≤ AI ≤ 0.070% 0.04% ≤ Nb ≤ 0.06% 3.4 × N ≤ Ti ≤ 8 × N 0.02% ≤ Cr ≤ 0.1% 0.0005% ≤ B ≤ 0.004% 0.001% ≤ S ≤ 0.009% It contains [a certain substance], with the remainder being iron and impurities resulting from the manufacturing process.

[0069] Preferably, the carbon content of the base material 3 of the first pre-coated steel sheet 1 is at least 0.05% by weight higher than the carbon content of the base material 4 of the second pre-coated steel sheet 2.

[0070] According to the present invention, the aluminum-containing precoats 7 and 8 of at least one of the first precoated steel sheet 1 and the second precoated steel sheet 2 contain at least 50% by weight of aluminum.

[0071] Preferably, the precoats 7 and 8 are obtained by hot-dip plating, i.e., by immersing the substrates 3 and 4 in a bath of molten metal. In this case, as shown in Figure 1, the precoats 7 and 8 include at least intermetallic alloy layers 9 and 10 that are in contact with the substrates 3 and 4.

[0072] The intermetallic compound alloy layers 9 and 10 contain an intermetallic compound comprising at least iron and aluminum. The intermetallic compound alloy layers 9 and 10 are formed particularly by the reaction of the substrates 3 and 4 with the molten metal in the bath. More specifically, the intermetallic compound alloy layers 9 and 10 contain Fe x -Al y The type includes, more specifically, intermetallic compounds of Fe2Al5.

[0073] In the example shown in Figure 1, the pre-coats 7 and 8 further include metal alloy layers 11 and 12 extending over the intermetallic compound alloy layers 9 and 10. These metal alloy layers 11 and 12 have a composition close to that of the molten metal in the bath. The metal alloy layers 11 and 12 are formed by the molten metal carried away by the plate as it passes through the molten metal bath during hot-dip plating.

[0074] The metal alloy layers 11 and 12 are, for example, layers of aluminum, layers of aluminum alloy, or layers of aluminum-based alloy.

[0075] In this context, an aluminum alloy refers to an alloy containing more than 50% by weight of aluminum. An aluminum-based alloy is an alloy in which aluminum is the main component by weight.

[0076] For example, the metal alloy layers 11 and 12 are layers of aluminum alloy further containing silicon. More specifically, the metal alloy layers 11 and 12 are by weight - 8% ≤ Si ≤ 11%, - 2% ≤ Fe ≤ 4% It contains [amount], with the remainder being aluminum and possible impurities.

[0077] The metal alloy layers 11 and 12 have thicknesses that fall between, for example, 19 μm and 33 μm, or between 10 μm and 20 μm.

[0078] In the example shown in Figure 1, where precoats 7 and 8 include metal alloy layers 11 and 12, the thickness of the intermetallic compound alloy layers 9 and 10 is generally around a few micrometers. In particular, their average thickness typically falls between 2 and 7 micrometers.

[0079] Specific microstructures of precoats 7, 8, including intermetallic compound alloy layers 9, 10 and metal alloy layers 11, 12 obtained by hot-dip plating, are disclosed in particular in patent EP2007545.

[0080] According to another embodiment, the aluminum-containing precoats 7, 8 comprise only the intermetallic alloy layers 9, 10 described above. In this case, the thickness of the intermetallic alloy layers 9, 10 is, for example, between 10 μm and 40 μm. Such precoats 7, 8 comprising the intermetallic alloy layers 9, 10 can be obtained, for example, by subjecting the precoats 7, 8, which include the intermetallic alloy layers 9, 10 and metal alloy layers 11, 12 disclosed above, to a pre-alloying treatment. Such a pre-alloying treatment is carried out at a temperature and holding time selected to alloy the precoats 7, 8 and the substrates 3, 4 over at least a portion of the thickness of the precoats 7, 8.

[0081] More specifically, the pre-alloying process includes the following steps: heating the plate to a pre-alloying temperature between 620 and 1000°C, and holding the pre-alloyed plate at this temperature for a time that varies from several minutes to several hours depending on the processing temperature used. In this case, the intermetallic compound alloy layers 9 and 10 themselves consist of Fe2Al5, FeAl3, FeAl, and Fe6Al 12 It can be composed of different intermetallic compound sublayers, such as Si5 and FeAl3 sublayers.

[0082] Advantageously, as shown in FIG. 1, the base materials 3, 4 are provided with the above-mentioned aluminum-containing precoats 7, 8 on both of their main surfaces.

[0083] The first and second precoated steel plates 1, 2 can carry the same precoats 7, 8.

[0084] Alternatively, the precoats 7, 8 of the first and second precoated steel plates 1, 2 may have different compositions.

[0085] Next, if a filler metal is used as appropriate, the theoretical average aluminum content in the welded joint 22 obtained by butt welding between the above-mentioned first and second precoated steel plates 1, 2 is determined.

[0086] When it is intended to use a filler metal, the filler metal is preferably a steel-based filler metal having an aluminum content of 0.05 wt% or less.

[0087] This determination is made by any method known to those skilled in the art.

[0088] For example, the theoretical average aluminum content in the welded joint 22 can be determined using the following formula.

Equation

[0089] The above formula can be used even when using a filler material, as long as the filler material contains an aluminum content of 0.05% by weight or less.

[0090] The above formula can also be used when base materials 3 and 4 contain aluminum, as long as the aluminum content of base materials 3 and 4 is 0.05% by weight or less.

[0091] The proportion β of steel-based filler material optionally added to the weld pool is, for example, between 0 and 0.5, i.e., the proportion is between 0 and 50% when expressed as a percentage.

[0092] Theoretical average aluminum content of welded joint 22 Al th weld If the amount would strictly exceed 1.25% by weight, the method according to the present invention further includes the step of preparing at least one welded edge 14 of the pre-coated steel sheets 1, 2 such that, after preparation, the theoretical average aluminum content of the welded joint falls between 0.5% by weight and 1.25% by weight.

[0093] More specifically, the welded edges 14 of the pre-coated steel sheets 1 and 2 are the edges of the pre-coated steel sheets 1 and 2 that are intended to be welded to the other pre-coated steel sheet 1 or 2.

[0094] As shown in more detail in Figure 3, the weld edge 14 includes peripheral portions of the pre-coated steel sheets 1 and 2 that are intended to be incorporated at least partially into the welded joint 22 during butt welding. More specifically, the weld edge 14 comprises a side surface 13 of the pre-coated steel sheets 1 and 2 and a portion of the pre-coated sheets 1 and 2 that extends from this side surface 13 and includes parts of the pre-coat 7 and 8 and parts of the base material 3 and 4.

[0095] More specifically, the process of creating the welded edge 14 includes removing the aluminum-containing precoat 7, 8 from at least one of the main surfaces 5, 6 of the first and second precoated steel sheets 1, 2 over a portion of its thickness. The precoat 7, 8 is removed from the side surface 13 of the precoated steel sheets 1, 2 over a removal zone 18 extending along the welded edge 14. The removal zone 18 can extend over a width between 0.5 mm and 2 mm from the side surface 13 of the precoated steel sheets 1, 2. An example of a precoated steel sheet 1 thus produced is shown in Figure 3.

[0096] Removal is preferably performed using a laser beam.

[0097] Advantageously, in the removal zone 18, the metal alloy layers 11 and 12 are removed, while the intermetallic compound alloy layers 9 and 10 remain over at least a portion of their thickness.

[0098] More specifically, in removal zone 18, the metal alloy layers 11 and 12 are removed, but the intermetallic compound alloy layers 9 and 10 are left intact.

[0099] The residual intermetallic compound alloy layers 9 and 10 protect the area of ​​the weld blank immediately adjacent to the welded joint 22 from oxidation and decarburization during the subsequent hot forming process, and from corrosion during use.

[0100] In the example shown in Figure 3, the metal alloy layers 11 and 12 are removed at the weld edge 14 across the removal zone 18, leaving the intermetallic compound alloy layers 9 and 10 intact.

[0101] In particular, the proportion of precoats 7 and 8 to be removed, and the number of main surfaces of precoated steel sheets 1 and 2 from which the precoats 7 and 8 should be removed, and the theoretical average aluminum content of the welded joint 22 after removal. th weld This is such that the amount falls between 0.5% by weight and 1.25% by weight.

[0102] In particular, pre-coat 7 and 8 are - On only one main surface 5, 6 of the first or second pre-coated steel sheet 1, 2, or - On a total of two main surfaces, for example, on one main surface 5, 6 of each of the first and second pre-coated steel sheets 1, 2, or on one of the two main surfaces 5, 6 of the first and second pre-coated steel sheets 1, 2, or - On a total of three main surfaces 5, 6, that is, on two main surfaces 5, 6 of one of the first and second pre-coated steel sheets 1, 2 and on only one main surface 5, 6 of the other pre-coated steel sheet 1, 2, or - On a total of four main surfaces 5, 6, i.e., on the two main surfaces 5, 6 of the first and second pre-coated steel sheets 1, 2 It can be removed over at least a portion of its thickness.

[0103] The theoretical average aluminum content of a welded joint 22 obtained by butt welding the first and second pre-coated steel plates 1 and 2 provided in the supplying process, using a filler material having an aluminum content of 0.05% by weight or less, if applicable. th weld However, if the amount is between 0.5% by weight and 1.25% by weight, welding is performed on the first and second pre-coated steel sheets 1 and 2 without removing the pre-coats 7 and 8 beforehand. More specifically, in this case, welding is performed using the first and second pre-coated steel sheets 1 and 2, and their pre-coats 7 and 8 remain as they are, at least on the weld edges 14.

[0104] The theoretical average aluminum content of the welded joint 22 obtained by butt welding between the first and second pre-coated steel sheets 1 and 2 provided in the supplying process, optionally using a filler material having an aluminum content of 0.05% by weight or less. th weld However, even if it falls between 0.5% by weight and 1.25% by weight, and more precisely even if it is greater than 0.5% by weight, the precoat 7, 8 may be removed over at least a portion of its thickness at the weld edge 14 on at least one main surface 5, 6 of at least one of the two precoated steel sheets 1, 2, for example, on only one main surface 5, 6 of at least one of the two precoated steel sheets 1, 2. For example, the precoat 7, 8 is removed over at least a portion of its thickness at the weld edge 14 on only one main surface 5, 6 of each of the two precoated steel sheets 1, 2. This optional removal step may be performed using a filler material having an aluminum content of 0.05% by weight or less to determine the theoretical average aluminum content of the welded joint 22 obtained by welding between the first and second precoated steel sheets 1, 2 thus produced. th weld However, the process is carried out in such a way that the concentration remains between 0.5% and 1.25% by weight.

[0105] In particular, such removal is performed at the heat treatment temperature T used in the subsequent heat treatment. t This may be carried out to further reduce the heat treatment temperature T t This is determined as described below. In fact, the austenitization temperature Ac3(WJ) of the welded joint 22 decreases with decreasing aluminum content. In particular, this optional removal step is determined by the heat treatment temperature T which is determined without removal. t This can be carried out when the temperature will strictly exceed 950°C. In fact, in order to maintain good paintability and weldability, the heat treatment temperature T should be 950°C or lower. t It is preferable to use [this].

[0106] Theoretical average aluminum content of welded joint 22 Al th weldAfter determining the manufacturing process, and if necessary or desired, the method further includes a step of butt welding the first pre-coated steel sheet 1 to the second pre-coated steel sheet 2 using laser welding to obtain a welded joint 22 between the first and second pre-coated steel sheets 1 and 2, thereby obtaining a welded steel blank 15.

[0107] The welded joint 22 has an aluminum content that is between 0.5 and 1.25% by weight.

[0108] According to one embodiment, the welding process includes the use of filler material.

[0109] A steel-based filler material with an aluminum content of 0.05% by weight or less is preferable. The filler material has a low aluminum content and dilutes the aluminum from the coating.

[0110] For example, the filler material further contains an austenite-forming element to partially balance the ferrite formation and / or intermetallic compound formation effect of aluminum from precoats 7 and 8.

[0111] The filler material is, for example, a filler wire or powder.

[0112] The proportion of filler material added to the weld pool is, for example, between 0 and 0.5.

[0113] For example, the filler material has the following composition by weight: 0.1% ≤ C ≤ 1.2% 0.01% ≤ Mn ≤ 10% 0.02% ≤ Ni ≤ 7% 0.02% ≤ Cr ≤ 5% 0.01% ≤ Si ≤ 2% Optionally, Trace amount≦Mo≦1% Trace ≦Ti≦0.1% Trace amount≦V≦0.1% Trace amount≦B≦0.01% Trace amount≦Nb≦0.1% Trace amount≦Al≦0.05% The remainder consists of iron and impurities that inevitably result from the manufacturing process.

[0114] In certain examples, the filler material may have one of the compositions W1, W2, or W3 listed in Table 1 below.

[0115] [Table 1]

[0116] In all of these compositions, the content is expressed as a weight percentage.

[0117] Furthermore, for each composition, the remainder consists of iron and unavoidable impurities.

[0118] In Table 1 above, "-" means that the composition contains at most a trace amount of that element.

[0119] In the modified version, the welding process is a self-welding process, which means that welding is performed without the use of filler material. In this case, the composition of the welded joint 22 depends only on the composition of the base materials 3 and 4 of the first and second pre-coated steel sheets 1 and 2, and the amount of pre-coating 7 and 8 incorporated into the welded joint 22.

[0120] The welding process results in the formation of a welded joint 22 at the junction between the two plates 1 and 2.

[0121] The welding process is a laser welding process, in which a laser beam 24 is directed towards the joint between two pre-coated steel plates 1 and 2.

[0122] Laser welding processes are carried out using, for example, CO2 lasers, solid-state lasers, or semiconductor lasers.

[0123] The laser source is preferably a high-power laser source. The laser source can be selected from, for example, a CO2 laser with a wavelength of 10 micrometers, a solid-state laser source or semiconductor laser source with a wavelength of 1 micrometer, or a diode laser with a wavelength between 0.8 and 1 micrometer.

[0124] The laser output is selected according to the thickness of the first and second pre-coated steel sheets 1 and 2. In particular, the output is selected to allow for sufficient mixing in the welded joint 22 as well as fusion of the welded edges 14 of the pre-coated steel sheets 1 and 2. For CO2 lasers, the laser output is, for example, between 3 and 12 kW. For solid-state or semiconductor lasers, the laser output is, for example, between 2 and 8 kW.

[0125] The diameter of the laser beam 24 at its impact point 26 on the pre-coated steel plates 1 and 2 can be equal to approximately 600 μm for both types of laser sources.

[0126] During the welding process, welding is performed, for example, under a protective atmosphere. Such a protective atmosphere prevents oxidation and decarburization of the area being welded, formation of boron nitride within the welded joint 22, and potential cold cracking due to hydrogen absorption.

[0127] The protected environment is formed, for example, by an inert gas or a mixture of inert gases. The inert gas can be helium, argon, or a mixture of these gases.

[0128] Welding may be performed using laser light as the sole heat source.

[0129] Optionally, the laser welding process includes an additional heat source in addition to the laser beam, such as an electric arc or induction heating. This additional heat source contributes to melting the edges of the first and second pre-coated steel sheets 1 and 2 to form the welded joint 22.

[0130] Optionally, the welding process includes the use of a filler wire 20, as shown by the dashed line in Figure 1. In this case, the laser beam 24 is additionally configured to melt the filler wire 20 at the impact point 26 of the laser beam 24.

[0131] During the welding process, the distance between the opposing weld edges 14 of the two pre-coated steel plates 1 and 2 is, for example, 0.3 mm or less, and more specifically, 0.1 mm or less. By providing such a gap between the opposing weld edges 14 of the two plates 1 and 2, material deposition from the filler wire 20 during the welding operation is promoted, preventing the formation of excessive thickness at the welded joint 22.

[0132] At the end of the welding process, a welded steel blank 15 is obtained as shown in Figure 2.

[0133] After the welding process, the method according to the present invention includes the step of heating the thus obtained welded steel blank 15 in a heat treatment oven.

[0134] More specifically, the heating process involves heat-treating the welded steel blank 15 at a heat treatment temperature T t This includes heating up to a certain point.

[0135] According to the present invention, the heat treatment temperature T t This is at least 10°C lower than the complete austenitization temperature Ac3(WJ) of the welded joint 22.

[0136] The complete austenitization temperature Ac3(WJ) of the welded joint 22 is expressed in °C and is determined from the composition of the welded joint 22 using, for example, the following formula. Ac3(WJ)=102.2×Al+439×C+181.9×Mn+364.1×Si+148×Al 2 -425.2 × C 2 -29.2 × Mn 2 -497.8 × Si 2-400×Al×C + 9.9×Al×Mn - 50.5×Al×Si - 208.9×C×Mn + 570.3, where Al, C, Mn, and Si respectively refer to the contents of aluminum, carbon, manganese, and silicon in the welded joint 22, and are expressed in wt%.

[0137] The above formula for Ac3(WJ) can be used within the content range shown in Table 2 below.

[0138] [Table 2]

[0139] In Table 2 above, - All contents are expressed in weight percent. - "-" means there is no lower limit value.

[0140] According to the present invention, the heat treatment temperature T t is at least 15°C higher than the lowest temperature T min . In this regard, the lowest temperature T min is defined as follows. [Equation] In the formula, Ac3(WJ) is the complete austenitization temperature of the welded joint 22, expressed in °C, Al is the content of aluminum in the welded joint 22, expressed in wt%, [Equation] In the formula, Ts1 is the maximum tensile strength of the strongest base material 3 after press hardening, expressed in MPa, Ts2 is the maximum tensile strength of the weakest base material 4 after press hardening, expressed in MPa, [[ID=​​​This is the carbon content of the filler material, expressed in weight percent. ρ is the ratio (ρ=t2 / t1) of the thickness of the pre-coated steel sheet 2 containing the weakest base material 4 to the thickness of the pre-coated steel sheet 1 containing the strongest base material 3.

[0141] In this regard, a substrate is weaker than others if it has a lower maximum tensile strength Ts after press curing.

[0142] Therefore, the lowest temperature T min This can be calculated based on the following: - Chemical composition of welded joint 22, - Characteristics of base materials 3 and 4 of pre-coated steel sheets 1 and 2 - When using filler material, specify the proportion and composition of the filler material.

[0143] The process of heating the welding blank 15 further involves heating the welding steel blank 15 to a heat treatment temperature T t This includes a holding process that takes place for a period of time between 2 and 10 minutes.

[0144] At the end of the heating process, the welded steel blank 15 is heated to a temperature at least 10°C lower than the complete austenitization temperature Ac3(WJ) of the welded joint 22, so the microstructure of the welded joint 22 is not completely austenitic. The transformation interval ferrite fraction in the welded joint 22 is determined by the heat treatment temperature T t It depends on the temperature difference between and the complete austenitization temperature Ac3(WJ) of the welded joint 22. In particular, at the end of the heating process, the ferrite fraction α of the transformation section in the welded joint 22 IC The ferrite fraction α is 15% or more and is the maximum transformation interval ferrite fraction α max IC At least 5% lower (15% ≤ α IC ≤α max IC -5%).

[0145] The ferrite fraction of the maximum transformation interval is expressed in percent and can be determined using the following formula.

number

[0146] As is known to those skilled in the art, the ferrite fraction in the transformation interval is, for example, the heat treatment temperature T t This can be measured by directly quenching the weld blank 15 after heating it to a certain temperature. After the adapted Nital etching, the transformed ferrite appears as a pale component on the grayish martensite matrix.

[0147] The transformation zone ferrite fraction of the welded joint 22 can also be determined by analyzing a manganese element mapping image of the sample, which shows the distribution of manganese content within the sample. Such a mapping image can be obtained, for example, by analyzing the sample using electron probe microanalysis (EPMA). In this Mn mapping image, regions showing a minimum Mn content coincide with the transformation zone ferrite region, while regions with higher Mn content correspond to phases resulting from the transformation of austenite formed during transformation zone annealing. Therefore, the surface fraction of the transformation zone ferrite corresponds to the surface fraction of the region with a minimum Mn content in this image. This method is described, for example, in Hanlon, D; Rijkenberg, A; Leunis, E et al.: Quantitative phase analysis of multi-phase steels, PHAST (2007), ISBN 92-79-02658-5, pp. 77-79. In fact, it is known that during transformation zone annealing, manganese distribution occurs between austenite and ferrite, with manganese moving from ferrite to austenite. As a result, at the end of transformation zone annealing, the Mn content of transformation zone ferrite is strictly less than that of austenite. Phases formed from austenite during subsequent cooling, such as martensite, transformation zone ferrite, and / or bainite, inherit the Mn content of austenite, while transformation zone ferrite retains its lower Mn content resulting from this distribution. Therefore, on a Mn element mapping image, transformation zone ferrite can be distinguished from other phases, particularly other types of ferrite, and corresponds to the region with the minimum Mn content.

[0148] In connection with this patent application, all proportions related to the microstructure are expressed as surface percentages.

[0149] At the end of the heating process, the microstructure of the base materials 3 and 4 of the first and second pre-coated steel sheets 1 and 2 is completely austenitic. In particular, because aluminum from the pre-coating 5 and 6 is present at the weld edges 14 of the pre-coated steel sheets 1 and 2 during welding, the complete austenitization temperature Ac3 of the base materials 3 and 4 is strictly lower than the complete austenitization temperature Ac3(WJ) of the welded joint 22.

[0150] At the end of the heating process, the welded steel blank 15 is hot-formed into a steel part in a press using a press forming tool. For example, the welded steel blank 15 is formed into a steel part by hot stamping using a suitable hot stamping tool.

[0151] Preferably, the transfer time between the heat treatment oven and the press forming tool is 10 seconds or less. The transfer time is, for example, between 5 and 10 seconds. The transfer time is selected to be as short as possible in order to avoid metallurgical transformation in the weld blank 15, particularly the formation of ferrite before hot forming.

[0152] The steel parts formed in this manner are then cooled at a cooling rate equal to or greater than the critical martensite or bainite cooling rate of the most hardenable base material 3, 4 among the base materials 3, 4 of the first and second pre-coated steel sheets 1, 2.

[0153] Advantageously, the cooling process is carried out by using a press forming tool that includes, for example, a cooling system comprising cooling channels formed within the press forming tool.

[0154] According to the present invention, at the end of the cooling process, the welded joint 22 is composed of martensite and / or bainite, and a ferrite fraction α of 15% or more, with a maximum transformation interval of ferrite. maxIC α is at least 5% lower than the transformation interval ferrite fraction α max IC (15% ≤ α IC ≤α max IC It has a microstructure containing -5%). Maximum transformation interval ferrite fraction α maxIC can be determined as described above.

[0155] At the end of the cooling process, at least one of the base materials 3 and 4 mainly has a martensite and / or bainite microstructure. Martensite and / or bainite result from the transformation of austenite formed during the heating process during the cooling process.

[0156] According to one example, both base materials 3 and 4 mainly have a martensite and / or bainite structure.

[0157] In this context, "mainly" means that the microstructure consists of martensite and / or bainite, and at most 5% ferrite.

[0158] The present invention also relates to a press-hardened laser-welded steel part obtained by using the above method.

[0159] This part is, in particular, a collision management part, for example, an intrusion prevention part or a shock absorption part, a structural part or a part contributing to the safety of an automobile.

[0160] The press-hardened laser-welded steel part comprises a first coated steel part portion and a second coated steel part portion joined by the weld joint 22 as described above.

[0161] More specifically, the first coated steel part portion and the second coated steel part portion are respectively due to hot press forming and cooling in the press forming tools of the first and second pre-coated steel sheets 1 and 2.

[0162] More specifically, each coated steel part portion includes a steel substrate having an aluminum-containing coat containing iron and at least 30% by weight of aluminum on at least one of its main surfaces.

[0163] In particular, the aluminum-containing coats of the first and second steel part portions result from at least partial alloying of the pre-coats 7 and 8 during hot press forming.

[0164] The base materials for the first and second steel component parts have the compositions described above for pre-coated steel sheets 1 and 2. These are produced by hot-press molding and cooling of the base materials 3 and 4 of the pre-coated steel sheets 1 and 2.

[0165] The base material of the first coated steel component has a maximum tensile strength Ts1 that is strictly greater than the maximum tensile strength Ts2 of the base material of the second coated steel component.

[0166] For example, the first coated steel component has a first thickness, the second coated steel component has a second thickness, and the product of the first thickness and the maximum tensile strength of the first coated steel component is strictly greater than the product of the second thickness and the maximum tensile strength Ts2 of the second coated steel component.

[0167] The welded joint 22 has an aluminum content between 0.5% by weight and 1.25% by weight.

[0168] The welded joint 22 is composed of martensite and / or bainite, with a ferrite fraction α of 15% or more and the maximum transformation interval α. max IC α is at least 5% lower than the transformation interval ferrite fraction α IC (15% ≤ α IC ≤α max IC It has a microstructure that includes -5%).

[0169] Maximum transformation interval ferrite fraction α max IC This can be determined as explained above.

[0170] On press-hardened laser-welded steel parts, the proportion β of filler material added to the weld pool during welding is determined by one of the applied methods, which is the aluminum content Al of the welded joint 22. weld This can be determined by measuring the aluminum content of the coating on welded steel plates. coating Knowing this, and considering that the amount of aluminum in the filler material can be ignored, the formula

number

number

[0171] The maximum tensile strength of the welded joint 22 is greater than or equal to the maximum tensile strength of the weakest base material 4 after press hardening.

[0172] At least one side of the welded joint 22, corresponding to the steel of the first base material 3, has a martensite and / or bainite structure. For example, the steel on both sides of the welded joint 22, corresponding to the steel of the first base material 3 and the steel of the second base material 4, has a martensite and / or bainite structure.

[0173] The inventors of the present invention have surprisingly found that when the weld blank 15 is heat-treated under the above conditions, the maximum tensile strength of the welded joint 22 becomes exactly greater than the maximum tensile strength of the base material 4 of the second pre-coated steel sheet 2, i.e., the base material having the lowest maximum tensile strength. Therefore, when a tensile test is performed in a direction perpendicular to the welded joint 22, the parts obtained after the heat treatment do not break at the welded joint 22, even though the structure of the welded joint 22 after heat treatment is not entirely martensite or bainite.

[0174] Therefore, the method according to the present invention is particularly advantageous because it can obtain satisfactory mechanical properties at low cost. In fact, when welding pre-coated steel sheets containing aluminum pre-coating together, it is no longer necessary to adjust the composition of the welded joint by, for example, removing the pre-coating from both sides of the pre-coated steel sheet or by adding a large amount of austenitizing elements to the weld using a filler material such as filler wire, so that the complete austenitization temperature of the welded joint is below the complete austenitization temperature of the base material. In particular, avoiding the removal of the pre-coating from both sides of the steel sheet shortens the total processing time. Furthermore, by reducing the amount of austenitizing elements that must be added by the filler material, or even by avoiding the use of filler material altogether, manufacturing costs are significantly reduced, and problems caused by the addition of high proportions of filler material, particularly related to the geometric shape of the welded joint and obtaining a uniform mixture between the material from the pre-coated steel sheet and the material from the filler material of the welded joint, are prevented. [Examples]

[0175] The inventors of the present invention conducted experiments E1 to E36 in which welded steel blanks 15 were fabricated using pre-coated steel sheets 1 and 2. Each pre-coated steel sheet 1 and 2 has a base material 3 and 4 having the following composition (see Table 5), and pre-coats 7 and 8 formed by hot-dip plating on both main surfaces, the pre-coats 7 and 8 containing metal alloy layers 11 and 12 comprising 88% by weight of aluminum, 10% by weight of silicon, and 2% of iron.

[0176] The total weight per unit area of ​​precoats 7 and 8 on the main surfaces of both precoated steel sheets 1 and 2 is 150 g / m², before any removal process. 2 That was the case.

[0177] After removing the metal alloy layers 11 and 12 from only one of the main surfaces 5 and 6 of pre-coated steel sheets 1 and 2, while leaving the intermetallic compound alloy layers 9 and 10 intact, the total weight per unit area of ​​the residual pre-coating 7 and 8 on each of the pre-coated steel sheets 1 and 2 is 100 g / m². 2 That was the case.

[0178] The composition of the substrate used in the experiment is disclosed in Table 3 below. The composition of the filler wire used in the experiment is shown in Table 4 below.

[0179] [Table 3]

[0180] [Table 4]

[0181] In Tables 3 and 4 above, the composition is expressed as a weight percentage.

[0182] Furthermore, for each composition in Tables 3 and 4, the remainder of the composition consists of iron and unavoidable impurities.

[0183] The hyphen "-" indicates that the composition contains at most a trace amount of that element.

[0184] The complete austenitization temperature Ac3 and maximum tensile strength Ts of the above substrates S1, S2, and S3 are as follows. S1: 834℃, Ts=1500MPa S2: 858℃, Ts=1050MPa S3: 806℃, Ts=700MPa

[0185] Pre-coated steel plates 1 and 2 were butt-welded using a 5.6kW disk laser or a 4kW YAG laser.

[0186] In all cases, a protective atmosphere consisting of helium or argon was used to avoid oxidation and decarburization of the welded area, as well as potential low-temperature cracks due to boron nitride formation and hydrogen absorption in the welded joint. The gas flow rate was 15 L / min or higher.

[0187] Next, the welding blank 1 is subjected to heat treatment at a temperature of 920°C T. tThe blank was heated to a certain temperature, held at this temperature for 6 minutes, transferred to a hot press forming tool with a transfer time selected to prevent ferrite formation between the heating oven and the hot forming tool, and then subjected to a heat treatment in which it was cooled in the press forming tool for 1 minute at a cooling rate of 30°C / second or more to obtain a press-cured blank.

[0188] The experimental conditions used in experiments E1 to E36 are summarized in Tables 5 and 6 below.

[0189] Next, tensile test specimens were cut from the heated blanks obtained in this manner, perpendicular to the welded joint.

[0190] Tensile tests were performed at ambient temperature (approximately 20°C) on longitudinal tensile test specimens of type EN 12, 5×50 (240×30 mm) drawn parallel to the rolling direction, using the methods disclosed in the following standards, namely NF EN ISO 4136 and NF ISO 6892-1. Five tensile tests were performed on each heated welded blank.

[0191] The results of the tensile test are shown in the column titled "Location of failure" in Table 6 below, which indicates where failure occurred during the tensile test.

[0192] In this section, - "BM" refers to the breakage of the base metal, that is, the breakage of one of the base materials of the pre-coated plate. - "Weld" refers to the failure of a welded joint. - "Mix" refers to a case where part of the tensile test specimen breaks at the welded joint, while other parts break at the base metal.

[0193] [Table 5] JPEG2026067925000020.jpg97150JPEG2026067925000021.jpg21150

[0194] In Table 5 above, 150g / m 2The pre-coat weight corresponds to the case where no fabrication process is performed before welding, i.e., the pre-coat remains on both main surfaces of the pre-coated steel sheet at the time of welding, whereas 100g / m 2 The pre-coated weight corresponds to the case where the pre-coated steel sheets are manufactured by removing the metal alloy layers 11 and 12 from only one main surface of each of the pre-coated steel sheets 1 and 2 before welding, leaving the intermetallic compound alloy layers 9 and 10 intact.

[0195] [Table 6] JPEG2026067925000023.jpg97150JPEG2026067925000024.jpg14150

[0196] In Tables 5 and 6 above, examples that do not conform to the present invention are underlined.

[0197] These results show that when the welding blank 15 is heated to a heat treatment temperature within the above temperature range, and the holding time before press forming and cooling is between 2 and 10 minutes at the heat treatment temperature, failure occurs in the weakest base metal of the assembly (the "base metal of the second pre-coated steel sheet" in Tables 5 and 6 above), but not in the welded joint 22 (Experiments E1, E2, E5, E10, E12, E13, E16, E18, E22 and E29-E32).

[0198] Conversely, the minimum heat treatment temperature T min For heat treatment temperatures strictly less than +15°C and holding times between 2 and 10 minutes at said heat treatment temperatures, failure is observed to always occur at the welded joint 22 (Experiments E3, E4, E6-E8, E14, E15, E17, E19, E21, E23, E27-E27 and E33-E36), or at least in some of the tensile test specimens at the welded joint 22 in the experiments examined (Experiments E9, E11, E20, E24 and E28, referenced "mix" in the table).

[0199] The inventors further stated that in all experiments according to the present invention, the welded joint 22 was 15%~αmax IC The fraction α of ferrite in the transformation interval, which is between -5%. IC We focused on the fact that it has a microstructure that includes [specific element].

[0200] These results demonstrate that when the weld blank 15 is heat-treated using the heat treatment conditions according to the present invention, the welded joint 22 has a maximum tensile strength that is strictly greater than the maximum tensile strength of the weakest base material corresponding to the base material 4 of the second pre-coated steel sheet 2. Therefore, it is this base material 4 that forms the weakest zone of the part, and not the welded joint 22. As a result, damage occurs in the base material 4 of the second pre-coated steel sheet 2, but not in the welded joint 22 itself. These results are surprising because they are obtained even though the welded joint 22 is not completely austenitized and therefore does not have a predominantly martensite and / or bainite microstructure after heat treatment.

[0201] Therefore, the method according to the present invention is particularly advantageous because it makes it possible to determine the optimal method parameters (including the minimum heat treatment temperature and the amount of filler material added) to obtain a part with satisfactory properties while minimizing manufacturing costs and time.

Claims

1. A method for manufacturing press-hardened laser-welded steel parts, comprising the following series of steps, namely - A step of providing a first pre-coated steel sheet (1) and a second pre-coated steel sheet (2), wherein each of the first and second pre-coated steel sheets (1, 2) includes a steel base material (3, 4), and at least one of the first and second pre-coated steel sheets (1, 2) has an aluminum-containing pre-coat (7, 8) containing at least 50% by weight of aluminum on at least one of its main surfaces. The first pre-coated steel sheet (1) has a first thickness (t １ The second pre-coated steel sheet (2) has a second thickness (t ２ ) has, The base material (3, 4) of the first pre-coated steel sheet (1) has a maximum tensile strength (Ts) after press curing compared to the base material (4) of the second pre-coated steel sheet (2). ２ ) Strictly greater than the maximum tensile strength (Ts １ ) has, First thickness (t １ ) and the maximum tensile strength (Ts) of the first pre-coated steel sheet (1) after press hardening. １ The product of ) is the second thickness (t ２ ) and the maximum tensile strength (Ts) of the second pre-coated steel sheet (1) ２ The product of the following is strictly greater than the supply process, then, - In the case of optionally using a filler metal containing at least 0.05% by weight of aluminum, the theoretical average aluminum content (Al ｔｈ ｗｅｌｄ ) in the weld joint (22) obtained by butt-welding the first and second pre-coated steel sheets (1, 2) provided in the providing step is strictly greater than 1.25% by weight, at least one aluminum-containing pre-coat (7, 8) on at least one main surface (5, 6) of at least one of the welding edges (14) of the first and second pre-coated steel sheets (1, 2) is removed over at least a part of its thickness, and as a result, in the case of optionally using a filler metal containing at least 0.05% by weight of aluminum, the theoretical average aluminum content (Al ｔｈ ｗｅｌｄ ) of the weld joint (22) obtained by butt-welding the first and second pre-coated steel sheets (1, 2) thus produced is included between 0.5% by weight and 1.25% by weight, a removing step, - A welding process in which a first pre-coated steel sheet (1) and a second pre-coated steel sheet (2) are butt-welded together using laser welding to obtain a welded joint (22) between the first and second pre-coated steel sheets (1, 2), thereby obtaining a weld blank (15), wherein the welding process may include the use of a filler material (20), a butt welding process. - Heat treatment the welding blank (15) at a temperature (T ｔ A step of heating up to the heat treatment temperature (T ｔ The temperature is at least 10°C lower than the complete austenitization temperature (Ac3(WJ)) of the welded joint (22), and the minimum temperature T ｍｉｎ At least 15°C higher, here, [Math 1] And in the formula, Ac3(WJ) is the complete austenitization temperature of the welded joint (22), expressed in °C, and Al is the aluminum content of the welded joint (22), expressed in weight percent. α ｍａｘ ＩＣ This is the ferrite content in the maximum transformation interval of the welded joint (22) calculated by the following formula: [Math 2] During the ceremony, Ts １ This is the maximum tensile strength of the strongest substrate (3) after press curing, and is expressed in MPa. Ts ２ This is the maximum tensile strength of the weakest substrate (4) after press curing, and is expressed in MPa. C ＦＷ This is the carbon content of the filler material, expressed in weight percent. β is the proportion of filler material added to the weld pool, and is between 0 and 1. ρ is the ratio of the thickness of the pre-coated steel sheet (2) containing the weakest base material to the thickness of the pre-coated steel sheet (1) containing the strongest base material (ρ = t ２ / t １ ) and The welding blank (15) is heat-treated to a temperature (T ｔ ) A process of holding the object for a time that falls within the range of 2 to 10 minutes. - A process of press-forming a welded blank (15) into a steel part, and - A step to obtain a press-hardened welded steel part from the steel part formed in this manner: Cooling the steel part at a cooling rate equal to or greater than the critical martensite or bainite cooling rate of the most hardenable base material among the base materials (3, 4) of the first and second pre-coated steel sheets (1, 2). A method that includes this.

2. After press curing, the maximum tensile strength (Ts) of the base material (3) of the first pre-coated steel sheet (1) is determined. １ ) and the maximum tensile strength (Ts) of the base material (4) of the second pre-coated steel sheet (2) ２ The method according to claim 1, wherein the ratio to ) is 1.2 or more.

3. The method according to claim 1 or 2, wherein the carbon content of the base material (3) of the first pre-coated steel sheet (1) is at least 0.05% by weight higher than the carbon content of the base material (4) of the second pre-coated steel sheet (2).

4. The method according to any one of claims 1 to 3, wherein each of the first and second pre-coated steel sheets (1, 2) provided in the supplying process includes an aluminum-containing pre-coat (7, 8) containing at least 50% by weight of aluminum on at least one of its main surfaces (5, 6).

5. The method according to any one of claims 1 to 4, wherein the first and second pre-coated steel sheets (1, 2) provided in the supplying step include an aluminum-containing pre-coat (7, 8) containing at least 50% by weight of aluminum on both of their main surfaces (5, 6).

6. The method according to any one of claims 1 to 5, wherein, during butt welding, the aluminum-containing precoat (7, 8) remains completely present on both main surfaces (5, 6) of at least one of the first precoated steel sheet (1) and the second precoated steel sheet (2), for example, the first and second precoated steel sheets (1, 2).

7. The method according to any one of claims 1 to 6, further comprising the step of producing a welded edge (14) of at least one of the first and second pre-coated steel sheets (1, 2) by removing the aluminum-containing pre-coat (7, 8) on at least one of its main surfaces (5, 6) over at least a portion of its thickness, even if the theoretical average aluminum content of the welded joint (22) obtained by butt welding the first and second pre-coated steel sheets (1, 2) provided in the supplying step is between 0.5% and 1.25% by weight, prior to butt welding.

8. For at least one of the first and second pre-coated steel sheets (1, 2), the steel of the base material (3, 4) is by weight, 0.10% ≤ C ≤ 0.5% 0.5% ≤ Mn ≤ 3% 0.1% ≤ Si ≤ 1% 0.01% ≤ Cr ≤ 1% Ti ≤ 0.2% Al ≤ 0.1% S ≤ 0.05% P ≤ 0.1% B ≤ 0.010% The method according to any one of claims 1 to 7, comprising iron and impurities resulting from the manufacturing process.

9. For at least one of the first and second pre-coated steel sheets (1, 2), the steel of the base material (3, 4) is by weight, 0.15% ≤ C ≤ 0.25% 0.8% ≤ Mn ≤ 1.8% 0.1% ≤ Si ≤ 0.35% 0.01% ≤ Cr ≤ 0.5% Ti ≤ 0.1% Al ≤ 0.1% S ≤ 0.05% P ≤ 0.1% B ≤ 0.005% The method according to claim 8, comprising iron and impurities resulting from the manufacturing process.

10. For at least one of the first and second pre-coated steel sheets (1, 2), the steel of the base material (3, 4) is by weight, 0.040% ≤ C ≤ 0.100% 0.70% ≤ Mn ≤ 2.00% Si ≤ 0.50% S ≤ 0.009% P ≤ 0.030% 0.010% ≤ Al ≤ 0.070% 0.015% ≤ Nb ≤ 0.100% Ti ≤ 0.080% N ≤ 0.009% Cu ≤ 0.100% Ni ≤ 0.100% Cr ≤ 0.2% Mo ≤ 0.100% Ca ≤ 0.006% The method according to any one of claims 1 to 9, comprising, with the remainder being iron and impurities resulting from the manufacturing process.

11. For at least one of the first and second pre-coated steel sheets (1, 2), the steel of the base material (3, 4) is by weight, 0.06% ≤ C ≤ 0.100% 1.4% ≤ Mn ≤ 1.9% 0.2% ≤ Si ≤ 0.5% 0.010% ≤ AI ≤ 0.070% 0.04% ≤ Nb ≤ 0.06% 3.4 × N ≤ Ti ≤ 8 × N 0.02% ≤ Cr ≤ 0.1% 0.0005% ≤ B ≤ 0.004% 0.001% ≤ S ≤ 0.009% The method according to any one of claims 1 to 10, comprising, with the remainder being iron and impurities resulting from the manufacturing process.

12. For at least one of the first and second pre-coated steel sheets (1, 2), the steel of the base material (3, 4) is by weight, 0.24% ≤ C ≤ 0.38% 0.40% ≤ Mn ≤ 3% 0.10% ≤ Si ≤ 0.70% 0.015% ≤ AI ≤ 0.070% 0% ≤ Cr ≤ 2% 0.25% ≤ Ni ≤ 2% 0.015% ≤ Ti ≤ 0.10% 0% ≤ Nb ≤ 0.060% 0.0005% ≤ B ≤ 0.0040% 0.003% ≤ N ≤ 0.010% 0.0001% ≤ S ≤ 0.005% 0.0001% ≤ P ≤ 0.025% It contains, and the titanium and nitrogen content satisfies the following relationship: Ti / N > 3.42 The carbon, manganese, chromium, and silicon content satisfies the following relationship: [Math 3] Steel contains one or more of the following elements in an optional manner: 0.05% ≤ Mo ≤ 0.65% 0.001% ≤ W ≤ 0.30% 0.0005% ≤ Ca ≤ 0.005% The method according to any one of claims 1 to 11, wherein the remainder is iron and impurities that inevitably result from the manufacturing process.

13. The method according to any one of claims 1 to 12, wherein laser welding is performed using a protective gas, particularly helium and / or argon.

14. The method according to any one of claims 1 to 13, wherein the first and second pre-coated steel sheets (1, 2) have different thicknesses.

15. The method according to any one of claims 1 to 14, wherein welding is performed without using filler material.

16. The welding is performed using a filler material, which preferably has the following composition by weight: 0.1% ≤ C ≤ 1.2% 0.01% ≤ Mn ≤ 10% 0.02% ≤ Ni ≤ 7% 0.02% ≤ Cr ≤ 5% 0.01% ≤ Si ≤ 2% Optionally, Trace amount≦Mo≦1% Trace amount≦Ti≦0.1% Trace amount≦V≦0.1% Trace amount≦B≦0.01% Trace amount≦Nb≦0.1% Trace amount≦Al≦0.05% The method according to any one of claims 1 to 14, wherein the remainder is iron and impurities that inevitably result from the manufacturing process.

17. A press-hardened laser-welded steel part, wherein the steel part includes a first coated steel part portion and a second coated steel part portion. Each coated steel component portion includes a steel base material, and at least one of the first coated steel component portion and the second coated steel component portion has an aluminum-containing coating containing at least 30% by weight of aluminum on at least one of its main surfaces. The first coated steel component portion has a first thickness (t １ ) has a second coated steel component portion having a second thickness (t ２ The base material of the first coated steel component portion has the maximum tensile strength (Ts) of the base material of the second coated steel component portion. ２ The maximum tensile strength (Ts) is strictly greater than ) １ ) has a first thickness (t １ ) and the maximum tensile strength (Ts) of the first coated steel component portion １ The product of ) is the second thickness (t ２ ) and the maximum tensile strength (Ts) of the second coated steel component portion ２ Strictly larger than the product of ) The first and second coated steel component parts are joined by a welded joint (22), the welded joint (22) having an aluminum content between 0.5% by weight and 1.25% by weight, and the microstructure of the welded joint (22) is martensite and / or bainite, and a ferrite fraction (α) between 15% and the maximum transformation interval. ｍａｘ ＩＣ The fraction of ferrite in the transformation interval (α) is composed of α between α and 5%. ＩＣ ) includes the maximum transformation interval ferrite fraction (α ｍａｘ ＩＣ ) is determined using the following formula, [Math 4] During the ceremony, Ts １ This is the maximum tensile strength of the strongest substrate (3) after press curing, and is expressed in MPa. Ts ２ This is the maximum tensile strength of the weakest substrate (4) after press curing, and is expressed in MPa. β is the proportion of filler material added to the weld pool, and is between 0 and 1. C ＦＷ This is the carbon content of the filler material, expressed in weight percent. ρ is the ratio of the thickness of the coated steel component portion containing the weakest base material to the thickness of the coated steel component portion containing the strongest base material (ρ = t ２ / t １ ) and and A press-hardened, laser-welded steel component in which at least one of the first and second coated steel component portions (3, 4) is a base material mainly having a martensite and / or bainite microstructure.

18. The final tensile strength (Ts) of the base material of the first coated steel component portion. １ ) and the final tensile strength (Ts) of the base material of the second coated steel component portion. ２ The press-hardened laser-welded steel part according to claim 17, wherein the ratio to ) is 1.2 or more.

19. For at least one of the first and second coated steel component parts, the base steel is by weight, 0.10% ≤ C ≤ 0.5% 0.5% ≤ Mn ≤ 3% 0.1% ≤ Si ≤ 1% 0.01% ≤ Cr ≤ 1% Ti ≤ 0.2% Al ≤ 0.1% S ≤ 0.05% P ≤ 0.1% B ≤ 0.010% A press-hardened laser-welded steel part according to claim 17 or 18, comprising, with the remainder being iron and impurities resulting from the manufacturing process.

20. For at least one of the first and second coated steel component parts, the base steel is by weight, 0.15% ≤ C ≤ 0.25% 0.8% ≤ Mn ≤ 1.8% 0.1% ≤ Si ≤ 0.35% 0.01% ≤ Cr ≤ 0.5% Ti ≤ 0.1% Al ≤ 0.1% S ≤ 0.05% P ≤ 0.1% B ≤ 0.005% The press-hardened laser-welded steel part according to claim 19, comprising, with the remainder being iron and impurities resulting from the manufacturing process.

21. For at least one of the first and second coated steel component parts, the base steel is by weight, 0.040% ≤ C ≤ 0.100% 0.70% ≤ Mn ≤ 2.00% Si ≤ 0.50% S ≤ 0.005% P ≤ 0.030% 0.010% ≤ Al ≤ 0.070% 0.015% ≤ Nb ≤ 0.100% Ti ≤ 0.080% N ≤ 0.009% Cu ≤ 0.100% Ni ≤ 0.100% Cr ≤ 0.2% Mo ≤ 0.100% Ca ≤ 0.006% A press-hardened laser-welded steel part according to any one of claims 17 to 20, comprising, with the remainder being iron and impurities resulting from the manufacturing process.

22. For at least one of the first and second coated steel component parts, the base steel is by weight, 0.24% ≤ C ≤ 0.38% 0.40% ≤ Mn ≤ 3% 0.10% ≤ Si ≤ 0.70% 0.015% ≤ AI ≤ 0.070% 0% ≤ Cr ≤ 2% 0.25% ≤ Ni ≤ 2% 0.015% ≤ Ti ≤ 0.10% 0% ≤ Nb ≤ 0.060% 0.0005% ≤ B ≤ 0.0040% 0.003% ≤ N ≤ 0.010% 0.0001% ≤ S ≤ 0.005% 0.0001% ≤ P ≤ 0.025% It contains, and the titanium and nitrogen content satisfies the following relationship: Ti / N > 3.42 The carbon, manganese, chromium, and silicon content satisfies the following relationship: [Math 5] Steel contains one or more of the following elements in an optional manner: 0.05% ≤ Mo ≤ 0.65% 0.001% ≤ W ≤ 0.30% 0.0005% ≤ Ca ≤ 0.005% The press-hardened laser-welded steel part according to any one of claims 17 to 21, wherein the remainder is iron and impurities inevitably resulting from the manufacturing process.

23. For at least one of the first and second coated steel component parts, the base steel is by weight, 0.06% ≤ C ≤ 0.100% 1.4% ≤ Mn ≤ 1.9% 0.2% ≤ Si ≤ 0.5% 0.010% ≤ AI ≤ 0.070% 0.04% ≤ Nb ≤ 0.06% 3.4 × N ≤ Ti ≤ 8 × N 0.02% ≤ Cr ≤ 0.1% 0.0005% ≤ B ≤ 0.004% 0.001% ≤ S ≤ 0.009% A press-hardened laser-welded steel part according to any one of claims 17 to 22, comprising, with the remainder being iron and impurities resulting from the manufacturing process.

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